A fuel cell, which is a main power supply of a fuel cell system, is a device supplied with oxygen corresponding to an oxidant and hydrogen corresponding to fuel to generate electricity while generating water. In the fuel cell, high purity hydrogen is supplied from a hydrogen storage tank to an anode of a fuel cell stack, and air including oxygen in the atmosphere is directly supplied to a cathode of the fuel cell stack by an air supply device such as an air compressor. Hydrogen supplied to the anode is separated into a proton and an electron by a catalyst of the anode and the proton is moved to the cathode through a polymer electrolyte membrane. Oxygen in the air supplied to the cathode combines with electrons introduced into the cathode through an external wire to generate electric energy while generating water.
Generally, the fuel cell stack includes a cell laminate formed by stacking at least several hundreds of unit cells, end plates disposed at both ends of the cell laminate, respectively, a fastening member that fastens the end plates to apply a predetermined surface pressure to the unit cells of the cell laminate, and the like. In particular, the term “unit cell” refers to a unit body formed by stacking a polymer electrolyte membrane, an anode, a cathode, a separator, a gasket, and the like.
Meanwhile, the surface pressure applied to the unit cells may be changed by various causes such as degradation of the fuel cell stack, contraction of the gasket due to a decrease in temperature, and the like. A change in surface pressure applied to the unit cells as described above becomes a main cause of deteriorating performance of the fuel cell stack such as gas leakage, a decrease in output power, deterioration of durability, or the like. However, since a fuel cell stack according to the related art does not include a configuration for compensating for a change in surface pressure applied to unit cells, performance of the fuel cell stack is deteriorated due to the change in surface pressure applied to the unit cells.